In computer systems, garbage collection refers to automated memory reclamation. Specifically, a garbage collector is a process that differentiates between live objects (i.e., objects that are still in use) and dead objects (i.e., objects that are no longer in use). Differentiating between live objects and dead objects typically involves traversing a graph of live objects to identify objects that should not be discarded.
Once live objects are identified, the garbage collector frees memory occupied by dead objects, and the freed memory is then available for other uses. In contrast, manual memory reclamation requires software developers to write code to explicitly free memory when objects are no longer needed. Errors in manual memory reclamation code may result in unnecessarily large memory footprints, memory leaks, etc. Thus, garbage collection reduces the probability of such errors occurring.
Garbage collection may be used in many different operating environments. For example, garbage collection may be used in a multitasking environment. A task is a set of executable instructions loaded into memory, and multitasking refers to situations in which multiple tasks are loaded into memory simultaneously. Specifically, each task is an isolated unit of execution and generally cannot access objects associated with other tasks. If a computer system includes only a single processor, only a single task can execute at a time. Still, execution may transfer from one task to another. For example, execution may transfer if an executing task reaches a stopping point, if a pending task has higher priority, if a maximum execution time is reached for an executing task, etc. In multi-processor computer systems, tasks may execute on each processor concurrently.